Manufacture of coated leather shaft seals



May 9, 1961 c. A. STEPHENS Erm. 2,983,131

MANUFACTURE 0F COATED LEATHER SHAFT SEALSv Original Filed Oct. 12, 19551... ALI-nl United States Patent O ll/IANUFACTURE OF COATED LEATHERSHAFI SEALS Clifford A. Stephens, Palo Alto, and Robert W. McCandless,Redwood, City, Calif.

Original application Oct. 12, 1955, Ser. No. 540,104,

now Patent N o. 2,854,267, dated Sept. 30, 1958. Di- ;lldzezmd thisapplication Feb. 3, 1958, Ser. No.

Claims. (Cl. 69-21) This invention relates to a method for coatingleather, especially leather shaft-sealing elements. This application isa division of our application Serial Number 540,- 104, filed October l2,1955, which has become Patent No. 2,854,267, which was acontinuation-in-part of our application Serial Number 519,862, filedJuly 5, 1955, now abandoned.

Leather has long been favored as far superior to most materials as apliant sealing element for shafts, reciprocating rods and the like.Despite this, it is recognized that leather has certain disadvantagesand fails to exhibit, to the degree desired, all the characteristicsneeded to meet the ever increasing requirements for a satisfactory seal.For example, leather varies widely in density, resilience, porosity andexibility, all of which affect performance and suitability for use assealing elements. Accordingly, over the years much eifort has beendirected toward improved processing procedures in an endeavor to providea product of more uniforml properties and longer service life. Inaddition, these attempts have included the augmentation of existingproperties as Well as the inclusion of new ones.

Another facet of the problemdervesrfrom the fact that certain desiredproperties of leather are customarily found only 4in combination withundesirable ones. For example, a leather having the desired ilexibilityis too soft to maintain good sealing contact with an eccentri` callyrotating shaft, or one which vibrates or whips as it rotates. Also, aflexible leather usually is quite porous. In consequence, it has a highreservoir capacity for lubricantan advantageous quality. But thisporosity is also attended by seepage of lubricant through the side wallsof the leather-a highly undesirable quality. Previous efforts to sealthe pores have destroyed the leathers capacity for storing lubricant andhave stiifened the leather objectionably.

The primary object of the present invention is the provision ofspecially processed leather in which the desirable properties of leatherare retained and augmented while other new properties areY added.

Another object is the provision of a sealing element having a main bodyof leather with a coating bonded to at least one surface and serving toseal that surface against loss of lubricant by seepage to reduce greatlythe surface friction, to increase the wearing qualities, and to add tothe mechanical strength of the leather but changing its stiffness onlyto a minimum degree.

Yet another important object is the provision of a shaft seal leathersealing element specially treated on its shaftfcontacting surface with alow-friction coating resistant to attack by lubricants and having longwearing qualities, whereby the torque loss caused by the seal is reducedto a minimum and the service life is increased.

ICC

A further object is the provision of a technique for coating leatherwith a veneer of elastomer applied as a liquid and allowed to dry beforethe application of heat and .pressure vulcanize the coating to thesurface area of the leather.

Still another object is a mode of vulcanizing and molding a ring areaonly of a plaque of leather whereby the unvulcanized center may betrimmed away and subsequently vulcanized and molded in a different sizeand shape.

Numerous other objects and advantages of the invention will becomereadily apparent from the following detailed specification taken inconnection with the accompanying drawings illustrating typical modes ofpracticing the invention, and wherein:

Figure l is a sectional view through a shaft seal in its installedposition and featuring a leather sealing member provided with alow-friction protective veneer on its outer surface only.

Figure 2 is` a fragmentary enlarged view through a similar seal buthaving a protective veneer on both'of its surfaces.

Figure 3 -is a fragmentary sectional view on a further enlarged scale,taken through the sealing member of Figure 2 and showing the thicknessof the coatings on an exaggerated scale for illustrative purposes only.

Figure 4 is a sectional View through a mold used in molding the leatherand vulcanizing the elastomeric surface veneer.

Figure 5 is a fragmentary view of the mold on an enlarged scale showingthe mold closed against a plaque of leather.

Figure 6 isA an isometric view, partly in section, of the leather as itappears after removal from the mold.

Referring to Figure 1, it will be seen that our uniquely coated leathersealing element may be used in a shaft seal of any suitableconstruction, such as the seal generally designated 1l). The radialflange 11 of our specially prepared leather sealing element is clampedbetween a metal washer 12 and the radial flange of a cupped outer case13, by means of a cup-shaped inner case 14. Thus, the in-turned edge 15of the casing 14 is held pressed against thewasher 12 by the curled-inrim 16 of the outer case 13. The exterior cylindrical surface 17 of theouter case is accurately finished so as to have a snug press-fit withthe side wall of a mounting bore 18 of -a shaft housing 19. Seatedagainst the shouldered inner end 20 of the bore 18 is a suitablebearing, such as an anti-friction bearing indicated at 21. This bearingmay be held seated in the bore, as by a split spring keeper ring 22,which seats in a groove formed in the bore wall. The bearing 21 servesto support a shaft 23 centrally of the mounting bore 16.

The flexible sealing member interposed between the shaft 23 and the sealcasing is formed principally of leather and is molded to provide anouter, radially extending, mounting flange 11 and a frusto-conical,axially extending, lip ilange 24. This general shape and form of leathersealing lip is conventional and has been in common use for many years.The smallest diameter portion of its inner edge 25 may be held insealing contact with the shaft 23 by a garter spring 26.

One of the unique features of the sealing element is the provision of athin film or veneer 27 of a special elastomer bonded to the inner orshaft-contacting surrather than the opposite fiesh side and to so mountthe seal in the housing bore y18 that -the elastomeric veneer is incontact with the shaft and is remote from the interior of the housing.rIhe reasons for this will become apparent presently. t

The principal Yfunctional ingredients of the veneer are a syntheticcil-resistant elastomer such as neoprene, a polyacrylic, a nitrile, or achlorosulfonated polyethylene rubber having a suitable drylubricant-dispersed therein, such as graphite, molybdenum disulfide,mica or talc. These substances, compounded along with a suitable solventVehicle in a `manner to be disclosed below, are applied in liquid formto the surface of the leather sealingmember and then vulcanized.

The elastomer does not penetrate beyond the base of the hair poreopenings or of the surface crevices and other imperfections of theleather. This confinement of the veneer to the immediate surface area ofthe leather and its absence from the many voids in the body of theleatherY is highly important and has several advantages. Thus, theabsence of elastomer from the interior body of the leather permits of afree and natural capillary flow p of lubricant Within the leather in apath generally parallel to the inner and outer surfaces. Secondly, themany voids naturally present in the leather are available as lubricantstorage reservoirs. And, thirdly, the inherent fiexi-bility of the bodyof the leather is not adversely affected by the presence ofincompressible particles filling the voids. And, of specialsignificance, the exterior sur' face of the leather or the one incontact with the rotating shaft 23 is sealed by a thin film of resilientmaterial which is highly resistant to attack by lubricants, relativelyimpervious to both liquids and gases, and has a coeiiicient of frictionat least 50% lower than the identical leather sealing element withoutthe surface coating of this invention. Y

A second embodiment of the invention is illustrated in Figure 2 anddiffers from the Figure 1 design in that both sides of the leathersealing element have a surface veneer of elastomer. The same referencecharacters have been used as in the first form but are distinguishableby the use of a prime. The -inner or iiesh side of the sealing elementis shown coated with a film of elastomer 28 corresponding to the coating27' on the outer or hair side. The film thicknesses are somewhatexaggerated in the drawing since, in practice, a film thickness of 2 `to5 mils has been found most eEective. Greater thicknesses can be employedbut :have a tendency -to stiffen the leather objectionably and are notfound to add to the service life of the sealing element to any materialextent.

Coating both sides of the sealing element has certain advantages. Itstiffens each side of the leather in equal degree; it provides a smoothfinished surface' on both sides of the sealing element; and it providesa substantially sealed reservoir for lubricant within the body ofleather proper. The outer lrim of this reservoir is sealed by thesurrounding housing for the sealing element, leaving only the innerperipheral edge exposed to the interior of the appliance housing and thesupply of oil therein. If the seal is to be used in a location notexposed to lub-ricating mediums, then the sealing element can besaturated with lubricant before installation. Thus, in either mode ofuse, the sealing edge of the lip has a continuous supply of oilavailable at all times. As soon as a film of oil between the shaft andthe contacting edge of the seal tends to disappear, it is immediatelyreplenished from the supply stored by capillary vaction in the body ofthe seal. Furthermore, the low friction coating in direct contact wththe shaft contains a dry lubricant locked within the coating. This drylubricantV supplements lthe liquid lubricant within the body of theseal-ing element.

The coating compositions which we have found to be Y so satisfactory forsurface films or coatings 27, 27 and 2S are elastomers or rubber-likesynthetics incorporating one or more dry lubricants that are dispersedtherein .to

impart lubricityA and other related properties important to a properlyfunctioning seal. For example, the coating elastomer may be neoprene GN,or neoprene GRT, standard elastomeric polymers of chloroprenecommercially available from E. I. du Pont de Nemours & Co. One hundredparts `of this material should be compounded for rapid curing and mixedwith between 10 and 60 parts by volume of a filling agent havinglubricating properties such as graphite, molybdenum disulfide, mica ortalc. (For graphite, the range by weight is between 20 and 120 parts per1GO parts elastomer.) This mixture is dissolved in a suitable solvent toprovide a lov,r Viscosity solution of 5-20% solids. If a lower solidscontent is employed, the film does not distribute uniformly to provide areliably continuous veneer, while a solution of higher solids content istoo viscous for satisfactory results. It will, of course, be understoodby those skilled in the handling of elastomeric compositions thatsuitable curing agents, antioxidants and accelerators are required asusual.

Suitable solvents include a mixture of one or more aromatics (toluene,benzene, or xylene and homologues of them) with parain hydrocarbons(e.g., gasoline or kerosene) or ketones (acetone, methyl-ethyl-ketone,and other -liquids of the group)l or naphthas. Wide vvariations ofquantities can be used, and which solvent mixture is selected willdepend on 4factors such as evaporation rate desired, cost,'toxicity,etc.

The `following specific examples suffice to illustrate the relativeproportions of constituents which have been found particularly suitablein actual practice:

EXAMPLE iV Neoprene rubber Constituents: 'Parts by weight Neoprene(chloroprene polymers) Magnesium oxide 4 Zinc oxide A 5Phenyl-alpha-naphthylamine 2 Z-mercaptoimidazoline l Graphite 30 Totalsolids 142' Methyl-ethyl ketone 1148 Toluene 130 Torn iiquids 127s Grandtotal 1420 Another composition giving excellent results employs`copolymers of butyl acrylate and acrylonitrile or ethyl acrylate andchloro-ethyl-vinyl ether in lieu of neoprene. Such a composition may becompounded as follows:

i A third composition makes use of nitrile elastomer instead ofneoprene. They following is an example of components by weight found inpracticeto give excellent results:

EXAMPLE Ill Nitrile elastomer Constituents: Parts by Weight Nitrileelastomer 100 Sulfur 2 Stearic acid 2 Zinc oxide 5Phenyl-alpha-naphthylamine 2 Tetramethyl thiuram disulfide V0.5 Graphite70 Terai solids 181.5 Methyl-ethyl-ketone 1470 Toluene 164 Total liquids1634 Grand total 1815.5

Still another composition which we have found to provide an excellentadherent veneer for leather employs chlorosulphonated polyethylene as aprincipal elastomeric component. This coating composition is made fromthe following ingredients:

1 Kenex B, Kenrich Corp.

In any of these four examples, mica, talc, and molyb denum disulfide maybe substituted for graphite, in equal volume. Graphite is, however,preferred.

Any of the foregoing compositions may be applied to the leather bydipping, dripping, spraying or other common coating techniques. However,since the deposition of a layer of the desired thickness and uniformityrequires contact with the liquid over an appreciable period of time,.the dipping and dripping-spraying techniques are particularlyadvantageous. Dipping is only practical when it is desired to coat bothsurfaces of the leather, while spraying may be used to coat either oneor both surfaces.

The dipping process may be carried out by immersing the leather into atank of the composition while the latter is agitated to keep the solidconstituents in suspension. Immersion should be continued for a periodof l0 to 60 minutes depending upon the thickness of coating desired. Theleather is then removed and allowed to drain and dry at room temperaturefor a period of 6 to 24 hours after which it is ready -for curing andmolding to the desired shape.

The spray coating and dripping procedures will be obvious yfrom therforegoing discussion of the dipping method. A spray, stream, ordripping of the coating liquid is applied to the leather for a period of10 to 60 minutes. Care is, of course, exercised to distribute thecoating composition evenly. If a coating is desired to only one surface,the spray or stream is directed in such a manner as to exclude it fromone side, and it may be dripped only on the upper surface. A preferredmethod is to carry a series of leather blanks or plaques along aconveyer, floating them on a lilm of the coating composition and passingthem below a series of dripping stations, each of which may comprise ahorizontal bar upon which the coating composition is being sprayed, sothat it drips over the edges onto the blanks passing below. During theperiod of exposure, .the low of composition is discontinued and thepieces are allowed to dry preparatory to curing and molding which may becarried out -by the aid of a vmold of the type illustrated in Figures 4and 6'.

Figure 4 shows a 2-part mold closed against a .plaque 4G of coatedleather. The mold includes a lower female member 41 secured to a heatedplaten 42 of a molding press by means of a cap screw 43. The cooperatingmale mold member 44 is similarly secured to an upper platen 45 by a capscrew 46. It will be observed that each of the mold members has a largearea cavity 47, 47 which does not contact the central portion 48 of theleather plaque. The outer opposed surface areas of the mold members 41and 44 have complemental sur-faces uniformly spaced from one another andshaped to `form a sealing element of L-shape in section as clearlyindicated in the several figures of the drawing.

The narrow radial surfaces 49 and S0 of the mold members grip the centerpart of the plaque 40 firmly and depress it into the general cup-shapedform shown in Figures 4 and 6 and hold it in this shape while theleather takes a permanent set and the elastomeric surface coatings arebeing vulcanized. The mold is closed under suicient pressure to compressthe leather from 20-3070 and so held for one minute while the molds aremaintained at a temperature of approximately 275 F. It will, of course,be appreciated that the pressure, molding period and temperature may bevaried over a considerable range as found to give the best results forthe particular leather and coating composition being used. Molding maybe carried out for longer periods (up to seconds) at lower temperatures,and shorter periods (down to 10 seconds) at high temperatures, buttemperatures higher than 325 F. should be avoided, else damage to theleather may result.

Slight curing of thecoating opposite the cavities 47, 47 of the moldmembers may occur from the limited amount of heat reaching this area ofthe coating composition. The mold is held closed for such a shortinterval that any curing which takes place will not interfere with thesubsequent moldingof a smaller size sealing element from the discardedcentral portion of the plaque 40. This will be best understood by thereference to Figure 6 showing the plaque 40 after it has been removedfrom the mold. The next step is to trim out the ring of leather desiredfor the sealing member. This is accomplished by placing the seal in atrimming lathe and cutting away the unvulcanized center along theconical surface indicated by a dotted line 50. The outer rim is likewisetrimmed at an angle such as that indicated by a dotted line 51. Thenarrow anged ring so produced forms the sealing element of the completedseal.

The salvaged central portion 4S of the disc may be used to formradial-washer type seals or another cupshaped sealing element of thesame general shape shown in Figure 2 but of smaller diameter. Hence, itwill be self-evident that this molding technique avoids Waste andpermits maximum usage of a given plaque of leather.

We claim:

1. That improvement in the treatment of leather for use as the flexiblesealing member in a shaft seal which comprises, exposing one side of aplaque of tanned leather to contact with a liquid mixture of a heatcurable exible elastomeric material and a dry lubricant in a confinedspace until a coating of the mixture to the desired thickness adheres tothe leather, drying the coating, forming a flanged cup from said plaque,subjecting the coating on the side wall and anged rim of said cup topressure and to heat not substantially in excess of 325 F. until said'elastomeric material is cured, and cutting away the bottom of said cupVto provide a flanged ring having a long- Wearing low-friction flexibleoil barrier coating adhering canizing said coating to the surface areaonly of said leather while simultaneously compressing the leatherapproximately 20% to 30% and While retaining it at a temperature notmaterially in excess of 325 F.

3. That improvement in the manufacture of shaft seals of the type havinga heat-molded leather sealing ring encased in a rigid mounting caseadapted to be pressed into a mounting bore surrounding a rotating shaftand comprising a leather ring having a radial ange and a flaring axialange joined to one rim edge thereof, the free rim edge of said flaringflange being adapted to have light pressure running contact with thesurface to be sealed against leakage of lubricant; said improvementcomprising the steps of coating the surface of` said leather intendedfor sealing contact before said leather ,is formed with said radial andaxial flanges with a fluent mixture consisting of an oil-resistantexible elastomer and graphite; and curing the coating for between aboutand 90 seconds at a temperature not substantially in excess of 325 F.while holding said leather deformed to provide the radial and axialflanges and while holding it cornpressed to an extent less than one-halfits natural state.

4. That improvement inthe manufacture of annularV molded leather ringswhich comprises coating at least one side of lsheet leather with a layerof iiexible elastomer dispersed in a solvent, drying the leather byexposure to air, molding a ring-shaped area onlyof the coated sheet to adesired shape under pressure and a temperature not substantially inexcess of 325 F. to vulcanize that portion of said coating underpressure, and trimming the molded and vulcanized portion of said ringfrom the unmolded and unvulcanized portion thereof.

5. That improvement in the manufacture of annular leather sealing ringsfor use in a shaft type seal which comprises coating the hair sideof asheet of leather with a liquid solution of uncured exible. elastomer,drying said coated sheet of leather, compressing and deforming a ringarea of said coated sheet Zbl-30% While leaving the remainder Vof the.sheet free of pressure, vulcanizing the elastomer in said ring area byheat, and trimming away the unvulcam'zed portions of the coatedleather'to either side of the vulcanized portion to provide an annularshaft sealing element having a thinresilient veneer of elastomer bondedto the hair side thereof.

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